What are the ten cloud genera?

The World Meteorological Organization recognises ten base cloud genera: cirrus, cirrocumulus, cirrostratus, altocumulus, altostratus, nimbostratus, stratocumulus, stratus, cumulus and cumulonimbus. Every cloud belongs to one of these basic types.

What do the altitude étages mean?

Clouds are grouped by the height of their base into étages: high (about 5 to 13 km), middle (2 to 7 km) and low (below 2 km). Cumulus and cumulonimbus span multiple levels and are classed as clouds of vertical development.

Which clouds signal rain?

Nimbostratus brings steady prolonged rain or snow, and cumulonimbus produces heavy showers, hail and thunderstorms. A spreading veil of cirrostratus often warns that a warm front and rain are approaching within a day.

What does the prefix or suffix mean?

Cirro- means high, alto- means middle, strato- means a flat layer and cumulo- means a heaped shape. The suffix -nimbus or prefix nimbo- marks a rain-bearing cloud, so nimbostratus is a rain-producing layer cloud.

Do genera have subtypes?

Yes. Each genus divides further into species describing shape and structure, such as cumulus humilis, and into varieties describing arrangement and transparency. This reference covers the ten base genera.

Cloud Classification Reference

Email me this result

Get this tool's output sent to your inbox, plus one useful tool a week. No spam, unsubscribe any time.

The ten basic cloud types

Every cloud in the sky belongs to one of ten genera defined by the World Meteorological Organization, organised by the altitude of the cloud base and by shape. This reference lists each genus with its abbreviation, altitude étage, appearance and the weather it tends to bring, plus filters by level and keyword so you can identify what you see overhead.

How it works

Cloud names combine a height prefix and a shape root:

cirro- = high      alto- = middle      strato- = layered (flat)
cumulo- = heaped   nimbo- / -nimbus = rain-bearing

High clouds (cirrus, cirrocumulus, cirrostratus) are made of ice crystals; low and middle clouds are mostly water droplets. Cumulus and cumulonimbus grow vertically across étages, with cumulonimbus reaching the tropopause and forming the classic anvil top of a thunderstorm. The étage filter restricts the list to high, middle, low or vertical clouds, and the keyword filter matches name, appearance or weather text.

Tips and notes

A halo around the sun or moon usually means cirrostratus and incoming rain.
A “mackerel sky” of small ripples is cirrocumulus.
Towering cumulus with an anvil top is cumulonimbus — expect storms.
Steady all-day rain comes from thick, featureless nimbostratus.
Each genus subdivides into species and varieties for finer description.